1. Field of the Invention
The present invention relates to the technical field of image processing and, more particularly, to a directional interpolation method for increasing resolution of an image.
2. Description of Related Art
Upon current TV broadcasting technology, odd and even display fields are alternately broadcasted due to limited bandwidth. Such a broadcasting method may lose even or odd lines of an image in every display field at the vertical direction, and thus a typical TV only displays odd or even lines of the image in scanning and displaying. However, new generation display systems such as liquid crystal displays (LCDs) have higher vertical resolution and thus obtain required high-resolution TV images by interpolation in vertical direction.
U.S. Pat. No. 5,001,563 granted to Doyle, et al. for a “Method of and circuit for processing a picture signal” discloses a method for processing a picture signal to interpolate a pixel by filtering the adjacent pixels. It focuses on the filter design, which only refers to the image pixels adjacent to the pixel to be interpolated. However, when it is applied to an image pixel with smoother gradient or thin slashes, the interpolated images may cause decision mistakes due to insufficient image messages, and accordingly the image with thin slashes is shown in zigzag and blur.
To overcome the aforementioned problem, U.S. Pat. No. 6,133,957 granted to Campbell; Jack J. for an “Adaptive diagonal interpolation for image resolution enhancement” discloses a method for using a least texture variance method to find one with the least texture variance from images to be interpolated as an interpolated image source, thereby increasing search distance. However, when the reference image distance is increased, a probability of image decision mistake is relatively increased and thus an unnatural image is generated. To avoid decision mistake problem, a confidence determination mechanism is added, which gives magnitude of confidence based on texture variance complexity of an image. When a low confidence is given, vertical direction is used as the interpolated image source, thereby avoiding decision mistake. However, such a way mostly uses vertical interpolation for a complicated image and thus the image shows discontinuousness.
Therefore, it is desirable to provide an improved interpolation method to mitigate and/or obviate the aforementioned problems.